Replacement refrigerant composition

ABSTRACT

A refrigerant composition for use in a vapour-compression refrigeration apparatus as a replacement for currently used refrigerants R22 and R12 comprises a mixture of pentafluoroethane (R125), tetrafluoroethane (R134a), a hydrocarbon selected from isobutane (R600a) and propane (R290), and optionally octafluoroethane (R218). The composition contains no chlorine atoms and is non-depleting to atmospheric ozone; but specific compositions have pressure-temperature relations substantially the same as R22 and R12 thereby allowing their use as direct replacements therefor in existing refrigeration apparatus.

TECHNICAL FIELD

The present invention relates to a refrigerant composition, whichcontains no chlorine atoms.

BACKGROUND

Chlorofluorocarbon (CFC) gases, such as refrigerant R12 (CCl₂ F₂), havebeen used for many years as refrigerants and are especially used indomestic refrigerators and car air conditioning systems. However, suchgases have been implicated in environmental damage. These gases, whichare very inert, are released from refrigeration systems at ground leveland diffuse into the upper atmosphere. Because of their inertness, thegases are able to survive without decomposition until they reach thestratosphere where they are broken down by ultra-violet radiation,releasing chlorine atoms which catalyse breakdown of the stratosphericozone layer. There has recently been considerable concern aboutreduction in stratospheric ozone levels and this has led to proposedrestrictions and prohibitions on certain CFC's.

Other refrigerants such as chlorodifluoromethane (R22) areenvironmentally less objectionable as they tend to be degraded naturallyat lower levels of the atmosphere before reaching the ozone layer.However, R22 contains chlorine and is still considered to contribute toozone depletion. Further, R22 has a higher index of compression than,for example, R12, such that compressor discharge temperatures becomeexcessive at pressure ratios which would not cause excessive dischargetemperatures if R12 were being used.

It is among the objects of the present invention to provide arefrigerant composition which does not contain any chlorine but whichhas acceptable refrigerant characteristics for use in vapour compressionrefrigerators as a replacement for refrigerant R22 and/or R12 inexisting refrigeration equipment.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention there is provided arefrigerant composition for use in a refrigeration apparatus whichcomprises a mixture of:

(i) pentafluoroethane;

(ii) tetrafluoroethane; and

(iii) a hydrocarbon selected from isobutane, propane and mixturesthereof.

The composition may optionally also contain (iv) octafluoropropane.

A further aspect of the present invention provides a method ofrefrigeration which employs the composition as a refrigerant medium,particularly a vapour-compression refrigerator.

A still further aspect provides a refrigeration apparatus which employsthe composition as a refrigerant medium, particularly avapour-compression refrigerator.

None of the components of the mixture contribute to ozone depletion norare any toxic to humans. Further, the mixture may be used with a varietyof existing lubricants as conventionally used in vapour compressionrefrigeration apparatus, including mineral oil lubricants, alkylbenzenelubricants and polyolester lubricants. Specialised lubricants are notrequired.

It is found that by forming mixtures of these three or four componentsin chosen proportions, it is possible to provide refrigerantcompositions which have pressure-temperature relationships which aresufficiently similar to those of the current refrigerants R22 and R12 toallow their use as replacements therefor in existing refrigerationequipment. The pressure-temperature relationship refers to the vapourpressure of the refrigerant composition at various temperaturescorresponding to those used in the refrigeration apparatus. Thus, thedesign pressure capabilities of the apparatus are not exceeded. It isalso found that the refrigeration capacities of the compositions of theinvention may be arranged to be similar to those of the currentrefrigerants R22 and R12, so that the refrigeration capacity (i.e. theamount of cooling produced) of refrigeration apparatus intended to beused with R22 or R12 respectively is substantially unaffected.

Advantageously, the compositions of the invention tend to have lowercompressor discharge temperatures than the corresponding conventionalrefrigerant.

The pentafluoroethane (R125) is preferably present in an amount of 0.5to 60 wt %, particularly 1 to 50 wt %. In compositions for use as an R22replacement, R125 is preferably present in percentages at the upper endof this range e.g. 20 to 45 wt %, particularly 27 to 40 wt %. Incompositions for use as an R12 replacement, the amount of R125 isusually at the low end of this range e.g. 0.5 to 10 wt %, especially 1to 10 wt. %.

The tetrafluoroethane (preferably R134a) is generally present in anamount of 30 to 98 wt %, particularly 30 to 90 wt. %, and usually formsthe major proportion of the composition. When used as an R22replacement, the composition of the invention usually employs 45 to 70%of R134a; whereas for use in replacing R12 the percentage of R134ausually lies in the range 80 to 90 wt. %.

For safety reasons, the hydrocarbon should preferably be present in anon-flammable proportion so that in the event of a leak of refrigerantmedium into the atmosphere, no explosive or flammable mixture isproduced. A hydrocarbon content of 1 to 11 wt %, particularly 2 to 10wt. %, and preferably 3 to 5 wt. % is preferred. In particular, anon-flammable composition is one which contains the components of themixture in such a ratio that when the composition is mixed with air inpractical proportions (e.g. in the event of a leak) no flammable mixtureresults. The fluorocarbon components R125 and R218 possessfire-retardant properties to a degree. Thus, the assessment offlammability characteristics is not necessarily predictable but can bedetermined by routine experimentation (see, for example, our patent U.S.Pat. No. 5,108,637).

The octafluoropropane (R218) is an optional constituent and is typicallypresent in an amount of 0 to 20 wt. %. It has a long lifetime whenreleased into the atmosphere so that future legislation may make its useless preferred. It is generally present in an amount of 4 to 15 wt %,particularly 5 to 10 wt. %.

DESCRIPTION OF PREFERRED EMBODIMENTS

In a preferred embodiment as an R22 replacement, the compositioncomprises a mixture of:

(i) 20 to 45 wt % pentafluoroethane (R125);

(ii) 45 to 70 wt % tetrafluoroethane (e.g. R134a);

(iii) 2 to 8 wt % isobutane (R600a); and

(iv) 5 to 10 wt % octafluoropropane (R218).

The pressure-temperature relationship of this mixture is similar to thatof chlorodifluorethane (R22). The refrigerating performance is alsosimilar within acceptable limits. However, the mixture has a lower indexof compression than R22, resulting in lower compressor dischargetemperatures, and of course contains no chlorine.

A preferred embodiment for use as an R12 replacement comprises a mixtureof:

(i) 0.5 to 5 wt % pentafluoroethane (R125);

(ii) 75 to 98 wt % tetrafluoroethane (R134a);

(iii) 1 to 6 wt % isobutane (R600a); and

(iv) 6 to 15 wt % octafluoropropane (R218).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the pressure-temperature diagrams for a compositionaccording to the invention (RX3) and conventional R22 refrigerant; and

FIG. 2 shows the pressure-temperature diagrams for a further compositionaccording to the invention (RX2) and conventional R12 refrigerant.

The composition according to the invention (RX3) comprised 40 wt. %R125, 6 wt. % R218, 50 wt. % R134a and 4 wt. % R600a and is intended asa replacement for currently used R22 refrigerant.

The composition in liquid form was introduced into an evacuated vesseland allowed to equilibrate. The vessel was heated to varioustemperatures and the vapour pressure in the presence of liquid noted. Itcan be seen from FIG. 1 that the pressure-temperature relationship isvery similar to that for R22, which means that the pressures encounteredusing the composition of the invention will not in substance exceedthose of R22. Thus the design pressures of the apparatus will not beexceeded.

FIG. 2 shows the pressure-temperature relationship for a furthercomposition (RX2) according to the invention in comparison toconventional R12 refrigerant. This was obtained following the proceduredescribed in relation to FIG. 1.

The composition (RX2) according to the invention comprised 1 wt % R125,9 wt % R218, 87 wt % R134a and 3 wt % R600a.

It will be noted that the pressure-temperature relationship for RX2 isvery similar to R12, so that it is suitable as a chlorine-freereplacement therefor without requiring substantial changes to therefrigeration apparatus.

EXAMPLE

A water chilling system in everyday use and employing refrigerant R12developed a leak at the hermetically sealed motor terminals. The leakwas repaired and the compressor replaced. The system was evacuated andrecharged with refrigerant composition RX2 according to the invention ofcomposition given above. Table 1 shows performance characteristicsbefore and after charging with RX2.

The performance using RX2 according to the invention is similar orslightly better than the performance using conventional refrigerant R12.

In Table 1 the abbreviations have the following meanings.

SUCT PRESS and DISCH PRESS are the compressor suction and dischargepressures, respectively.

SUCT TEMP COMP and DISCH TEMP EVAP COIL are compressor suction anddischarge temperatures, respectively.

SUCT TEMP EVAP COIL is the suction temperature at the evaporator coil.

LIQ TEMP BEFORE and AFTER HEAT EXCH are the respective temperaturesbefore and after the heat exchanger.

                                      TABLE 1                                     __________________________________________________________________________    (WATER CHILLER - REFRIGERANT RX2 as replacement for R12)                                               LIQ    LIQ                                                      SUCT                                                                              DISCH                                                                             SUCT  TEMP   TEMP   WATER                                     SUCT                                                                              DISCH                                                                             TEMP                                                                              TEMP                                                                              TEMP  BEFORE AFTER  TANK                                      PRESS                                                                             PRESS                                                                             COMP                                                                              COMP                                                                              EVAP COIL                                                                           HEAT EXCH.                                                                           HEAT EXCH.                                                                           TEMP                                   R12                                                                              psig                                                                              psig                                                                              °C.                                                                        °C.                                                                        °C.                                                                          °C.                                                                           °C.                                                                           °C.                             __________________________________________________________________________    1  30  140 16  57.7                                                                              12.7  30.5   11.5   13.2                                   2  28  130 15.8                                                                              62.4                                                                              8.5   28.5   11.0   9                                      3  22  130 13  65  4.9   28     12.4   4.5                                    RX2                                                                              NEW COMPRESSER AND REFRIGERANT CHARGE                                      1  20  140 14  69  4     38     33     3.5                                    2  20  150 14  74  6     38     36     3                                      3  20  145 13  70  4.5   37     36     2.5                                    4  20  143 13  69  4.6   37     35.5   2.7                                    5  30  155 16  70  10.1  35     28     8                                      6  20  143 13  69  4     36     30     3                                      __________________________________________________________________________

I claim:
 1. A refrigerant composition for use in a refrigerationapparatus which comprises a mixture of:(i) 1-50 wt % pentafluoroethane;(ii) 30-90 wt % tetrafluoroethane; and (iii) isobutane in an amountgreater than zero and less than an amount which would make the mixtureflammable.
 2. A composition according to claim 1 wherein the isobutaneis present in an amount of 1 to 11 wt %, and the composition isnon-flammable.
 3. A composition according to claim 2 wherein theisobutane is present in an amount of 2 to 10 wt %.
 4. A compositionaccording to claim 1 which comprises up to 20 wt % of octafluoropropane.5. A composition according to claim 4 wherein the octafluoropropane ispresent in an amount of 5 to 10 wt %.
 6. A refrigerant composition foruse as a replacement for refrigerant R22 in a refrigeration apparatuswhich comprises a mixture of:(i) 20 to 45 wt % pentafluoroethane; (ii)45 to 70 wt % tetrafluoroethane; (iii) 2 to 8 wt % isobutane; and (iv) 5to 10 wt % octafluoropropane.
 7. A refrigerant composition for use as areplacement for refrigerant R12 in a refrigeration apparatus whichcomprises a mixture of:(i) 0.5 to 5 wt % pentafluoroethane; (ii) 75 to98 wt % tetrafluoroethane; (iii) 1 to 6 wt % isobutane; and (iv) 6 to 15wt % octofluoropropane.